Python Dictionary

• Accessing Values in Dictionary:

  #!/usr/bin/python
  dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
  
  print "dict['Name']: ", dict['Name'];
  print "dict['Age']: ", dict['Age'];

• Output

  dict['Name']: Zara
  dict['Age']: 7

• Updating Dictionary:

  #!/usr/bin/python
  dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
  
  dict['Age'] = 8; # update existing entry
  dict['School'] = "DPS School"; # Add new entry
  
  
  print "dict['Age']: ", dict['Age'];
  print "dict['School']: ", dict['School'];

• Output

  dict['Age']: 8
  dict['School']: DPS School

• Delete Dictionary Elements:

  #!/usr/bin/python
  
  dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
  
  del dict['Name']; # remove entry with key 'Name'
  dict.clear(); # remove all entries in dict
  del dict ; # delete entire dictionary
  
  print "dict['Age']: ", dict['Age'];
  print "dict['School']: ", dict['School'];

• Output

  This will produce following result. Note an exception raised, this is because after del dict dictionary does not exist any more:
  
  dict['Age']:
  Traceback (most recent call last):
  File "test.py", line 8, in < module >
  print "dict['Age']: ", dict['Age'];
  TypeError: 'type' object is unsubscriptable

• Properties of Dictionary Keys:

  (a) More than one entry per key not allowed. Which means no duplicate key is allowed. When duplicate keys encountered during assignment, the last assignment wins. Following is a simple example:
  
  #!/usr/bin/python
  
  dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'};
  
  print "dict['Name']: ", dict['Name'];
  
  When the above code is executed, it produces following result:
  
  dict['Name']: Manni
  
  (b) Keys must be immutable. Which means you can use strings, numbers, or tuples as dictionary keys but something like ['key'] is not allowed. Following is a simple example:
  
  #!/usr/bin/python
  
  dict = {['Name']: 'Zara', 'Age': 7};
  
  print "dict['Name']: ", dict['Name'];
  
  When the above code is executed, it produces following result:
  
  Traceback (most recent call last):
     File "test.py", line 3, in < module >
     dict = {['Name']: 'Zara', 'Age': 7};
  TypeError: list objects are unhashable